Internal combustion engines having a relatively small number of cylinders provide automobile makers with an attractive solution to the need for improved fuel economy. In order to compensate for reduction of cubic capacity vehicle manufacturers developed technologies to improve engine power, such as direct fuel injection, turbocharging, and variable timing for inlet and exhaust camshafts. In this way six- and eight-cylinder engines can be scaled down without losing available horsepower.
An undesirable consequence of engines with a small number of cylinders is high crankshaft torsional vibration that is transmitted to the engine mounts and to the drive line. This results in higher seat track and steering wheel NVH as well as gear rattle.
Engineers manage these vibrations to one extent or another through a variety of approaches, many of which increase the cost of construction but reduce fuel economy. One accepted solution to overcome excessive vibration is the provision of one or more pendulums on the crankshaft to lower the torsional vibration of the crankshaft and the consequent vehicle noise and harshness. Such crankshaft-mounted pendulums function as vibration absorbers as they are tuned to address and thus reduce vibrations generated by oscillating torque, thus smoothing torque output of the crankshafts. This approach is taken as well by designers of some airplane piston engines where the pendulums smooth output torque and reduce the stress of the rotors.
An example of a pendulum vibration absorber associated with an engine crankshaft is set forth in U.S. Pat. No. 4,739,679, assigned to the assignee of the instant application. According to the arrangement set forth in this patent, a pendulum includes an inner curved cam follower surface that is alternately engaged and disengaged from a pin type cam fixed on the pendulum carrier.
The crankshaft pendulum and pendulum carrier used today are expensive to manufacture due to both material cost and machining cost. They must be made of steel for durability and, thus, are formed from hot forgings. Conventional pendulums include two such steel forgings that are bolted together. The individual steel forgings must be machined before assembly. The high cost of known pendulums and their associated carriers serve as a financial impediment to the wide-spread use of pendulums on crankshafts.
Thus a new approach to the pendulum crankshafts and their associated carriers is needed to address the problems associated with known arrangements.